The present invention relates to the flow of fluids into a patient""s blood stream and, more particularly, to a system and method for the volumetric measurement of fluids administered in any standard gravity intravenous infusion set.
The intravenous infusion of fluids into a patient""s bloodstream is a common medical procedure. Fluids that are typically administered intravenously include glucose and saline solutions, drugs, and blood. Intravenous (IV) systems generally comprise a reservoir, a drip chamber, a feed tube, and an IV needle. The reservoir, also called an IV bag, holds a quantity of the fluid to be infused. The reservoir is coupled to a dripper by means of a feed tube. The dripper, in turn, is coupled by the feed tube to the hollow IV needle, which is injected into a vein of the patient. The fluid in the reservoir drips through the needle and into the bloodstream, with the drip rate being controlled by the dripper.
In the past, two major approaches have been used to control the rate at which fluids are administered intravenously. The first approach is to use a conventional drip chamber which is manually controlled to adjust the drop rate through the drip chamber until the drops fall at a predetermined rate. This approach brings with it the advantage of simplicity in that only gravitational forces are needed to maintain the flow of fluids through the drip chamber.
However, manually controlled drip chambers are not satisfactory for all applications, for such drip chambers can permit fluid flow rate inaccuracies above or below the requested flow rate. These inaccuracies are due to the fact that the size of individual drops passing through the drip chamber can vary from set to set, the flow rate with which the fluid passes through the drip chamber, fluid pressure, and vibrational influences on the drip chamber. Furthermore, unless the drip chamber is carefully made to exacting tolerances, the drop volume may vary from one drip chamber to the next and definitely from one type of set to the next type. This means that a drop rate appropriate for a preselected fluid flow rate with a first drip chamber is not necessarily appropriate for a second drip chamber. Moreover, because of cold flow of tubing used in conjunction with conventional pinch clamps, a conventional, manually controlled drip chamber which is operating at a desired drop rate initially may well vary from this drop rate in time.
In an effort to provide greater accuracy of infusion rates, positive displacement infusion pumps have come into widespread use. Such pumps provide the advantage of accurately controlled infusion rates, largely independently of the pressure or the viscosity of the fluid being infused. However, such infusion pumps suffer from their own disadvantages. Because they typically operate at pressures of up to 60 psi, the danger of overpressure infusion is always present. Furthermore, infusion pumps tend to be relatively expensive, as well as heavy and cumbersome. In large part, the weight of infusion pumps is related to the size of the back up battery needed to power the pump in the event of a power failure. Because pumps operate motors on a regular basis, back up batteries for infusion pumps require large capacity.
The most basic part of control is to first obtain a precise volumetric measurement of the fluid administered.
U.S. Pat. No. 4,525,163 to Slavik et al teaches a flow control device including a sensor for measuring drop sizes. The drop sizes are measured as a calculation of averages after a certain number of optically detected drops fall into a burette. This is not a volumetric measurement and an additional drawback is that the administered fluid has to pass through the device, this being an invasive device.
U.S. Pat. No. 4,504,263 to Steur et al describes an invasive flow monitor where the flow of fluid passes through the monitor. The disadvantage of the invasive devices is that they have to be sterilized between uses and that becomes the responsibility and a resulting nuisance of the hospital requiring multiple devices with extras for sterilization. In the device described by Steuer the individual drops are measured by a infrared sensor. An additional drawback to the invasiveness of Steuer""s invention is that he assumes that the drops are spherical which is not always the case.
There exist prior art describing non-invasive devices for counting drops such as described in U.S. Pat. No. 6,083,206 to Molko. Molko teaches a device that can count drops with great precision by sensing infra-red radiation passing through the drip chamber, but does not account for the volumetric measurement of each drop and must rely on the drop size designated by the particular set.
The necessity for volumetric precision becomes critical for tiny infants who receive even less than two milliliters of fluid administered in an IV drip per hour.
As infusion pumps and gravity fed intravenous sets have the abovementioned disadvantages it would be highly advantageous to have a simple gravity fed intravenous set devoid of the above limitations.
According to one aspect of the present invention there is provided a device for the volumetric measurement of a fluid administered in a gravity infusion set including a drip chamber. The device includes a housing configured for releasable deployment around a cylindrical surface of the drip chamber. The housing includes a source of radiation configured to emit radiation through the drip chamber in a path substantially perpendicular to an axis of the cylindrical surface and an optical receiver deployed to be adjacent to a portion of the cylindrical surface substantially opposite the source of radiation. The optical receiver is configured for quantitatively sensing the radiation and a processor operative to calculate a volume of each drop passing through the drip chamber as a function of the relative loss of radiation quantitatively sensed by the receiver during passing of a drop against a background radiation.
According to another aspect of the present invention there is provided a method for calculating a volume delivered through an intravenous set with a drip chamber configured for the flow of the fluid substantially along the drip chamber""s axis. The method includes the steps of passing radiation from the exterior of the drip chamber through the drip chamber via a path generally perpendicular to the drip chamber axis to a sensor positioned on an opposite position on the exterior of the drip chamber, detecting and quantifying a background radiation value passing through the drip chamber, detecting and quantifying a radiation value passing through a drop falling through the drip chamber in order to obtain data indicative of a radiation loss due to the drop passing though the radiation path; and calculating a volume of the drop as a function of the relative loss of radiation detected during passing of the drop against the background radiation value.
According to yet another aspect of the present invention there is provided a method for calculating a volume delivered through an intravenous set with a drip chamber configured for the flow of the fluid substantially along the drip chamber""s axis. The method comprises the steps of passing radiation from the exterior of the drip chamber through the drip chamber via a path generally perpendicular to the drip chamber axis to a sensor positioned on an opposite position on the exterior of the drip chamber, detecting and quantifying a background radiation value passing through the drip chamber, detecting and quantifying a radiation value passing through a drop falling through the drip chamber in order to obtain data indicative of a radiation loss due to the drop passing though the radiation path; and deriving a volume measurement for the drop using a lookup table, the lookup table formed by accumulating empirical data.
According to further features in preferred embodiments of the invention described below, the radiation is configured to function in pulsed mode.
According to still further features in the described preferred embodiments the radiation is configured to function in continuous mode.
According to further features in preferred embodiments of the invention described below, the radiation is light radiation.
According to still further features in the described preferred embodiments the radiation is infra-red radiation.
According to still further features in the described preferred embodiments a volume calculated is used for controlling the flow of a fluid administered in a gravity infusion set.
According to still further features in the described preferred embodiments a relative loss of radiation is converted into a volume with the aid of a lookup table. The lookup table is created by accumulating empirical data of drops passing through various infusion sets determining a relative loss of radiation during the passing of the drop through the radiation and then weighing the drops and determining the volume of each drop in proportion to its specific gravity. The device and method is suitable for use with any IV set and is non-invasive.
The present invention successfully addresses the shortcomings of the presently known configurations by providing a device and method for measuring the volume of a drop, which can be used to determine the volume of a fluid administered in a gravity infusion set.